Human monocytes will be isolated by counterflow centrifugation and then incubated in a media that contains virtually no cholesterol but which promotes cholesterol loss from cells. The cholesterol loss and 3-hydroxy-3 methylglutaryl coenzyme A reductase activity of cells from normals, persons with familial hypercholesterolemia and other forms of hypercholesterolemia will be determined in an effort to devise a technique for the determination of familial hypercholesterolemia.